Question

花了8个小时来检查这个问题，但没有任何结果，有人说错了什么？

>SELECT id FROM posts AS post_id;SET categories.id  AS category_id;  
>SELECT title, contents, date_posted, categories, name FROM posts INNER JOIN 
>categories ON categories, id = posts, cat_id ORDER BY id DESC

并收到错误消息 $＃1193 - 未知的系统变量＆＃39; id＆＃39;

我也尝试这样的事情：

>SELECT id FROM posts AS post_id;  
>SELECT id FROM categories AS category_id;  
>SELECT COALESCE (title, contents, date_posted, categories, name) 
>FROM posts INNER JOIN categories ON categories, id = posts, cat_id
>ORDER BY id DESC

许多其他工作人员都没有正常工作。

工作查询：

 >SELECT posts . p_id AS post_id, categories . c_id AS category_id,  
    >title, contents, date_posted, categories . name   
    >FROM posts  
    >INNER JOIN categories ON categories . c_id = posts . cat_id  
    >ORDER BY posts.p_id DESC;

Answer 1

如果我理解您的查询，请按以下方式使用 -

  create table #ordered_products
(id int identity(1,1),
 grouping int default 0,
 Description varchar(128),
 level int,
 is_active bit);

 insert into #ordered_products (Description, level, is_active)
 select description, level, is_active from products;

-- All rows now have an order

declare @grouping int = 0;
declare @currentid int;
declare @found bit = 1;
declare @level int;
declare @base int;

set @currentid = (select min(id) from #ordered_products);

-- Go through all the rows setting a new group each time we hit level 1

while (@found = 1)
begin
  set @level = (select level from #ordered_products where id = @currentid);

  if (@level = 1)
  begin
    set @grouping = @grouping + 1
  end

  update #ordered_products set grouping = @grouping where id = @currentid

  set @currentid = @currentid + 1;
  set @found = (select 1 from #ordered_products where id = @currentid);

end

-- For each group, set the children to be inactive if the parent is

declare @maxgroup int = (select MAX(GROUPING) from #ordered_products);

declare @currentgroup int = 1;

while (@currentgroup <= @maxgroup)
begin

    begin
        set @base = (select MIN(id) from #ordered_products where is_active = 0 and grouping = @currentgroup);

        if (@base > 0)
        begin
            update #ordered_products set is_active = 0 where grouping = @currentgroup and id > @base;
        end
    end 

    set @currentgroup = @currentgroup + 1;  
end 

-- Output

select * from #ordered_products where is_active = 1;

drop table #ordered_products;

注意：您可以根据cat.id进行订购，然后相应地进行更改。

Answer 2

尝试将数据库中的变量名称ID更改为其他名称。 id是保留名称。

＃1193 - 未知的系统变量＆＃39; id＆＃39;

2 个答案: